I. Field of the Invention
The present invention relates generally to screeds and strike-offs for placing, screeding, finishing and shaping plastic concrete. More particularly, the present invention relates to a dynamic system for elongated finishing tools and concrete tools that can be selectively extended or retracted to avoid obstacles.
II. The Prior Art
As recognized by those skilled in the concrete finishing arts, after concrete is initially placed during construction, the upper surface must be appropriately finished. The purpose of finishing is to give the concrete a smooth, homogeneous and correctly textured surface and appearance. Various finishing devices, including screeds, have long been in use throughout the industry for treating plastic concrete. Known prior art systems include "bull" floats, finishing boards, strike-offs, pan floats, plows, blades and the like.
Strike-offs contact rough, freshly placed plastic concrete with a rigid leading edge to initially form and grade fresh concrete. Bull floats, comprising a flat, wooden board attached to a handle, can be manipulated by a single worker. Screeds are elongated tools employing a leading strike-off or blade that are moved over the concrete. They may employ flotation means, or they may ride forms. Modern screeds allow several finishing steps to be accomplished in a single pass.
Those skilled in the art will recognize that the selected finishing equipment must be appropriately matched to the job. For example, the type of equipment must be chosen based on the condition of the concrete. If high slump concrete is to be screeded, a floating pan would be ideal. For finishing drier concrete, a heavier twin-bladed screed might be more desirable. In all cases it is desirable to automatically insure level finishing.
The selection of an appropriate blade design for a particular screed is based upon a variety of factors related to the concrete involved. The characteristics of a particular batch of concrete depend upon the type and percentage of aggregate, and the quality and quantity of sand, cement, ad-mix, water and chemical additives forming the mix. Other variables, such as temperature, slab thickness, slump and placement method also affect blade selection and the application procedure.
It is an established fact in the art that vibration facilitates concrete finishing and consolidation. Many vibrating systems are presently in use in the industry. Vibration during screeding helps to settle or consolidate the concrete, thus eliminating air voids. Additionally, it helps to densify and compact the concrete during finishing. Vibrational screeding also draws out excess water, which increases the cured strength of the placed concrete. A fine layer of component cement and sand aggregate is raised to the surface with the excess water. This slurry aids in the subsequent fine finishing of the concrete and promotes the attainment of a uniform product.
I hold several patents in the art of concrete placement and finishing. U.S. Pat. No. 4,349,328, teaches a self-propelled "triangular truss" screed that rides upon forms. U.S. Pat. No. 4,798,494 discloses a floating vibratory screed that finishes concrete with or without forms. Finally, U.S. Pat. Nos. 4,316,715; 4,363,618 and 4,375,351 and the various references cited and discussed therein are germane to the general technology discussed herein. All the above patents have been assigned to the same assignee as the present case.
U.S. Pat. Nos. 4,650,366 and 4,386,901 disclose screeds capable of formless, self-supporting or floating operation. The latter patent discloses a triangular truss screed operated by two workmen without the use of forms. U.S. Pat. No. 4,650,366 discloses a light weight, portable vibrating screed including a central, extruded beam element.
U.S. Pat. No. 4,431,336 discloses a vibrating finishing screed for use upon plastic concrete that apparently is capable of floating. U.S. Pat. No. 2,314,985 discloses a vibratory hand screed including a central, vibrated pan for use upon plastic concrete without forms. Other prior art screeds, generally of the "form-riding" type, that are of general relevance include those screeds disclosed in U.S. Pat. Nos. 4,340,351; 4,105,355; 2,651,980; 2,542,979; 3,095,789; 2,693,136; and 4,030,873.
Stilwell, U.S. Pat. No. 4,427,358, discloses a coupling for eccentrically weighted driveshafts for vibratory screeds. This coupling employs a spring biased collar to captivate and join two semicylindrical shaft segments.
Other important considerations when planing a job include the manpower and logistics necessary to perform the required work. Concrete must often be placed and finished in relatively confined spaces. For example, the floors within a building are often placed after the majority of the structural elements are erected. Therefore, a contractor may well find it necessary to finish a floor after the erection of several disruptive structural elements. Often open areas are interrupted by structural members such as columns, beams, ductwork, or other similar protrusions. Although known screeds are generally convertible in length by breaking the screed down and removing or replacing sections, the work is tedious and expensive.
It is desirous to provide a screed that readily clears obstacles without adding or removing sections. It is further advantageous to provide a screed that can bypass columns and obstructions during finishing operations. It is desirable that the bypass readily lock in a deployed position in axial alignment with the rest of the screed and its elements (i.e., strike-off, pan float and/or bull float) when necessary. Additionally, the bypass should readily lock in a retracted, passive position.